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For more than a generation, the northern Lebanese town of Tripoli has been a divided city, home to most of Lebanon's Shia Alawi community, but also a stronghold of Sunni conservatism.

The two sects, in their respective neighbourhoods of Jebel Mohsen and Bab al-Tabbaneh, have been at odds since the outbreak of the Lebanese Civil War in 1975, with hundreds dying in the worst bloodshed in 1986. The road separating the two entrenched factions - appropriately called Syria Street - is the only demarcation line that still exists in Lebanon 22 years after the war ended.

In recent months, the outbreak of conflict in Syria and the influx of thousands of Syrian refugees into Lebanon has renewed and increased those tensions between Shia Alawis generally supportive of Syrian President Bashar al-Assad and Sunni sympathizers of the rebel Free Syrian Army (FSA) and the opposition.

More than 30 Lebanese from both sides have been killed in fighting between the two communities since the beginning of the Syrian uprising in March 2011. While a fragile ceasefire in Tripoli - agreed in early June - seems to be generally holding, sporadic clashes happen on a daily basis and it is common to see civilians carrying weapons.

While there are clear risks of Lebanon being caught up in the Syrian conflict, the reverse is also true: Syrian antagonists are equally in danger of being dragged into age-old Lebanese sectarianism.

The Syrian conflict has already killed at least 10,000, according to UN Secretary-General Ban Ki-Moon, and displaced as many as 500,000 people inside the country, according to the Syrian Arab Red Crescent, and another 86,000 are registered refugees in neighbouring countries. Basic services are not running properly, and the economy has been hard hit, not only by the conflict, but by far-reaching economic sanctions, pushing up unemployment and the price of food. Lebanon, which has already suffered decades of war, is rife with poverty and political instability. Both countries have much to lose.

Socio-economic factors and politics

Sectarianism and political antagonism in Tripoli have already had very real consequences for ordinary people on both sides.

Mahmud, a local vendor in the alleyways of Tripoli's market, points to the Alawi-owned shop next door, recently set on fire.

"The owner of this burnt shop paid the price of feuds between rogues," he explains.

"If these unbelievers want Bashar al-Assad, they can go to Syria," bursts out Omar, a long-bearded youngster, when asked about the shop. The risks for civilians here are large, with some Sunnis openly admitting that Alawi civilians could be further targeted.

"Now they don't dare to leave their mountain, we would beat them again," boasts Faysal, a talkative shopkeeper in Tripoli's market, who praises his cousin fighting in Bab al-Tabbaneh. "Those Alawis who are still in the city centre are Syrian workers, not Lebanese," he continues. "No one would harm them. But in case of a civil war, they will be killed, because wars know no ethical rules."

If history is anything to go by, those made destitute by the clashes are more likely to be dragged into violence. As the International Crisis Group put it in a briefing in October 2010, for many Sunni youngsters in Bab-Tebbaneh, joining one of the many Islamist groups which have spread relatively freely since Syria's military withdrawal provides an attractive alternative to idleness and social failure."

Lebanese politicians have been accused of exploiting the frustration of these poor neighbourhoods, supplying them with weapons.

"External actors transferred their conflicts there [in Tripoli], backing local fighters in a struggle that was less costly, and more easily managed, than would be open warfare in the capital…, just as… local fighters use their struggles… to attract important outside support," the 2010 Crisis Group briefing said.

Distrust in Lebanese army, intelligence

An enormous banner hanging in one of Tripoli's main squares, al-Tell, reads: "In defence of the security and stability of Tripoli". The whole city is plastered with these kinds of slogans. But behind the confident veneer, some residents are skeptical of the army's ability to maintain the peace.

From behind a small stand on a street corner, a coffee vendor named Khaled says he doesn't have much faith in the military.

"What do you want them to do? They stand aside!" he says laughing.

Weapons and Koranic commentaries pack the living room in the flat of Sheikh Bilal al-Masri, a Sunni leader fighting on Bab al-Tabbaneh's front line. He says the army - which usually limits itself to standing between both sides - started doing its job when, on one occasion recently, it responded to gunfire coming from Alawi-majority Jebel Mohsen. But he stresses that the military remains divided by political rivalries.

Residents of Jebel Mohsen are also skeptical of the army's ability to ensure their security.

"To us, [weapons] are more important than food," Rifa'at 'Eid, head of the pro-Assad Arab Democratic Party (ADP), told the Lebanese daily Al-Akhbar. "We have confidence in the army, but it cannot ensure our safety under certain conditions."

The Lebanese army is generally considered a "spectator" in armed clashes, because party militias such as Hezbollah are much better equipped, and because Lebanese politics are so divided. Prime Minister Najib Mikati's current government, as well as the Military Intelligence (mukhabarat al-jaysh) and the General Security (al-amn al-'aam) are believed to be aligned with Damascus, whereas the Internal Security Forces (quwwat al-amn al-dakhili) and its Information Branch (far' al-ma'lumat) are closer to the opposition Saudi-backed 14 March coalition, analysts say.

Syrian opposition and Lebanese Sunnis: between sympathy and military alliance

In Tripoli's government hospital, the tension is palpable. A nurse at the hospital showed IRIN bullet holes on the wall of one of the rooms overlooking Jebel Mohsen, suggesting the targets were the Sunni Syrian patients. The latter do not dare poke their heads out the window, for fear of being shot. The 50 Syrians in the hospital claim to be civilians, but the line between the armed opposition and the peace demonstrators is increasingly blurred.

Still, Tripoli remains one of the safest destinations in Lebanon for mostly Sunni Syrian refugees, due to the Sunni support for the uprising; and Lebanon has been a transit route for relief supplies into Syria. But analysts are increasingly questioning whether the ties between Lebanese and Syrian Sunnis go beyond mutual sympathy to military cooperation.

Samir*, a 23-old Syrian from Homs, now a member of a Syrian grouping of humanitarian and civil society organizations in Lebanon called Watan (Homeland), says there are clear boundaries to his involvement in the Bab al-Tabbaneh-Jebel Mohsen clashes: "If a Lebanese civil war breaks out, we will leave. We're not here to export our revolution. We need Lebanon as a basis for our activities."

Walid*, 27, who works for another humanitarian group, the Coordination Committees for Syrian Refugees' Affairs in Lebanon, holds different views on the relations between Syrians and Bab al-Tabbaneh: "I wanted to volunteer as a fighter in Bab al-Tabbaneh, but they rejected me.

"I wanted to do it, because the Alawis from Jebel Mohsen were involved in killing demonstrators in my city, Homs," explains Walid. "They came to support Alawis in Homs and slaughtered our people."

Al-Masri, the Sunni leader, confirmed having turned away Syrian volunteers. But he says the links between pro-Syrian government forces on both sides of the border are stronger. He says Lebanese Alawis are supplied with weapons and supported on the ground by Syrian and Hezbollah officers.

Pro-Syria media give a different view of the situation, with an article in pro-Hezbollah Lebanese daily Al-Akhbar accusing Riyadh al-Asaad, commander of the rebel Free Syrian Army, of visiting Tripoli to survey the territory, looking for an "ideal buffer zone".

Al-Masri denies both the existence of a 300-man Lebanese-Sunni unit within the FSA in Syria (as recently reported by Nicholas Blanford, Middle East analyst and author) and the presence of FSA camps in Lebanon. "We sent our men to Syria and they were rejected. They told us: 'We don't need you, but give us weapons, if it's possible'." He does admit to smuggling weapons and food to the FSA across the Lebanese border, by bribing Syrian officials.

Both the FSA and the pro-Syrian alignment led by Hezbollah have their reasons to deny having trespassed national borders. The first fears being blamed for igniting the existing tensions within Lebanon; the latter wants to prevent a new explosion of Sunni resentment. In a nutshell, no one wants to be blamed for a new Lebanese civil war.

But in the absence of a quick settlement with Jebel Mohsen, tensions in both countries are becoming increasingly intertwined, with analysts predicting that Lebanese Sunnis will eventually make use of their brethren across the border to fight their domestic enemies, namely Hezbollah. Already, tit-for-tat kidnappings have blurred the lines between the two conflicts, with Syrian Sunnis involved in kidnapping Lebanese Shias; Syrian officers involved in kidnapping Lebanese Sunnis; and Lebanese Sunnis involved in kidnapping Lebanese Alawis.

Who benefits from the clashes?

Analysts say both sides in Lebanon have something to gain from the clashes.

The anti-Syrian Future Movement (FM), headed by the former Lebanese Prime Minister Sa'ad al-Hariri, forced out of office in January 2011, has used the clashes as an opportunity to call for the current Prime Minister's resignation, arguing he has not been able to ensure Tripoli's security.

But in the eyes of Bab al-Tabbaneh's fighters, as well as many analysts, the Syrian government has more to gain.

"The first interest of the Syrian regime is distracting the attention of the media from what's going on in Syria," al-Masri says. "Secondly, Bashar wants to pressure the international community by saying he's capable of causing a civil war in Lebanon."

Both Bab al-Tabbaneh's fighters and ADP's spokespersons told the Lebanese newspaper The Daily Star that Hezbollah is supplying weapons to both Alawis and Sunnis in Tripoli, suggesting that the goal is to destabilize Lebanon - regardless of the victor - in order to draw attention away from the situation in Syria.